It is conventional practice to display an image obtained by an X-ray CT or the like on the screen of a CRT and record the displayed image by means of a multiframe photographic recording apparatus. This method involves problems in terms of, for example, resolving power, image distortion and fluorescent noise, since the CRT is employed as a medium. For this reason, medical image recording apparatuses which are arranged to record an image directly on a silver halide film by means of a laser beam scanning system have appeared. Unlike the conventional type of apparatus in which the image displayed on a CRT is recorded on a film (referring to silver halide photosensitive materials including photographic paper in this specification), this new type of apparatus is designed to record an image directly on a film by means of a laser beam which has been subjected to analog modulation.
FIG. 3 shows one example of the basic arrangement of this type of medical image recording apparatus. The reference numeral 1 denotes a He-Ne laser, 2 a lens, and 3 a prism. Light which is emitted from the laser 1 is passed through the lens 2 and bent 90.degree. by the prism 3 before entering an acoustooptic modulator 4, where the laser light is modulated by an ultrasonic wave modulated by information concerning the light and shade of an image so as to form light which carries information concerning the light and shade of the image. This light is then passed through a beam expander 5 and a prism 6 to enter a polygon mirror scanner 8 after the toppling angle has been corrected by a toppling angle correcting optical system 7. The polygon mirror scanner 8 is arranged such that a mirror is rotated and incident light is reflected by the rotating mirror so as to scan a recording film 9 laterally in order to record an image on the film 9. On the other hand, longitudinal scanning is effected by feeding the film 9 through a film feed mechanism 10.
The above-described medical image recording apparatus has advantages such as excellent resolving power, less image distortion and no fluorescent noise since it does not employ a CRT as a medium.
This medical image recording apparatus suffers, however, from the following problems. As will be clear from FIG. 3, the apparatus uses mechanical scanning mechanisms for main and subsidiary scanning operations, that is, the mechanism for rotating the polygon mirror scanner 8 for effecting abscissa scanning as main scanning and the recording film feed mechanism for effecting subsidiary scanning. Therefore, the number of movable portions is relatively large, which is disadvantageous in terms of reliability and transport durability. Further, the optical path length from the laser light source to the film is considerably long, so that it is difficult to arrange the apparatus so as to have a compact structure even though the mirrors are used to bend the beam in order to prevent the optical path from elongating in one direction.